The present invention relates to a process for preparing a granular hydrohalide salt of a particular metal complex compound which is composed of a divalent metal cation as central ion and of an amino dicarboxylic acid ion and, where appropriate, water as ligand, where the hydrohalide salt is obtained with a specific particle size distribution.
Complexes of a divalent metal cation as central ion and of an amino dicarboxylic acid ligand, and the hydrohalides thereof and various processes for preparing them are known. Complexes of a divalent metal cation as central ion and of an amino dicarboxylic acid ligand, for example magnesium L-aspartate can be handled substantially without problems. In contrast thereto, the hydrohalides thereof, especially magnesium L-aspartate hydrochloride, are usually very hygroscopic, so that they can be prepared only at extremely low humidity. Magnesium L-aspartate hydrochloride liquefies even at a humidity of more than 50 %, making its further processing extremely difficult or even impossible. Further processing to tablets or granules is accordingly possible only in air-conditioned zones with controlled low humidity. Because of the extreme hygroscopicity, it has been possible to date to granulate in particular magnesium L-aspartate hydrochloride only using organic solvents, which is undesired for environmental reasons.
In order to solve the problem of the hygroscopicity of the hydrohalides described above, attempts have been made to prepare a granular product with a reduced total surface area. All attempts made to date to prepare a granular product by spray drying have, however, provided an inadequate, usually very finely powdered material which, because of the large surface area or the high proportion of very finely powdered material, rapidly assumes a honey-like consistency, making further processing impossible. For example, a very finely powdered material is obtained under the spray-drying conditions (air inlet temperature: about 180° C.; air outlet temperature: about 120° C.) indicated in DE 32 38 118 A1 (cf. Examples 1 to 5 of DE 32 38 118 A1).